Implantable artificial heart

ABSTRACT

An implantable artificial heart (without extra-corporal circulation) includes a prime mover consisting of a Rankine or Hirn steam engine and a boiler heated by a radioisotopic source. A relaxation mechanism is interposed between the piston of the engine and a hydraulic transmission device and comprises a spring enclosed between two components which are respectively connected to the driving piston and to the driving member of the hydraulic device. Abutment means limit spreading apart of said components to a value at which the compression of the spring corresponds to maintenance of the blood pressure normally prevailing at the end of the systole phase. The component which is connected to the driving piston is temporarily locked at the end of the forward stroke of the piston and unlocked upon substantially complete expansion of the spring.

United. States Patent Lavigne [45] May 23, 1972 [54] IMPLANTABLE ARTIFICIAL HEART 3,434,162 3/1969 Wolfe ..3/1 3,534,409 10/1970 Lance et al. ...3/DIG. 2 [72] Invent Imam France 3,563,028 2/1971 Goranson et a1 ..3/1 [73] Assignee: Commimariat a LEnergie Atomlque,

Paris, Fr Primary Examiner-Channing L. Pace AttorneyCameron, Kerkam & Sutton [22] Filed: Dec. 21, 1970 21 Appl. No.1 100,255 [571 ABSTRACT 7 An implantable artificial heart (without extra-corporal circulation) includes a prime mover consisting of a Rankine or Him [30] Foreign Application Monty Data steam engine and a boiler heated by a radioisotopic source. A Dec. 31, 1969 France ..6945780 relaxation mechanism is interposed between the piston of the Aug. 12, 1970 France ..7029726 engine and a hydraulic transmission device and comprises a spring enclosed between two components which are respec- [52] US. Cl. ..3/1, 128/1 R, 128/214 R, tively connected to h ri ing pis n and to the driving 417/395, 417/401 member of the hydraulic device. Abutment means limit 51 Int. Cl ..A6lf 1/24, A61m 1/03, F04b 45/00 spreading apart of Said components to a value at which the [58] Field of Search ..3/1 DIG. 2; 128/l R, 214 R; compression of the spring corresponds maintenance of the 417/395 401 blood pressure normally prevailing at the end of the systole phase. The component which is connected to the driving [56] References Cited piston is temporarily locked at the end of the forward stroke of the piston and unlocked upon substantially complete expan- UNITED STATES PATENTS sion of the p 3,379,19l 4/1968 Harvey .128/1 R 18 Claims,6Drawing figures Patented May 23, 1972 4 Sheets-Sheet 2 FIG? I FHIMJZ HI 283/33 Pat ented May 23, 1972 4 Sheets-Sheet l) Patented May 23, 1972 4 Sheets-Sheet 4 FIGS IMPLANTABLE ARTIFICIAL HEART This invention relates to an implantable artificial heart, that is to say without extra-corporal circulation, which is capable of functioning independently over long periods of time without intervention. The condition just mentioned makes it necessary in practice to use an energy source consisting of an alpha radioelement, provided that the source is also implanted. It is thus possible to obtain operating times of the order of at least several tens of years without anyneed for intervention.

Installations for extra-corporal circulation are used almost exclusively at the present time and are substituted for a failing heart only during short periods and on such occasions, for example, as a surgical operation performed on the heart. A number of researches are also being devoted to implantable artificial hearts and have led to fairly satisfactory results in re gard to the pumping means which are substituted for at least one right ventricle or which assist this latter. On the other hand, much less progress has been made in the development of systems for actuating said pumping means. A number of implantable devices are at present being studied throughout the world but there is not one instance of a device which has reached a satisfactory stage of development.

The main difficulties which are encountered arise from the fact:

that the overall sizes and weights must be of a very small order: 2 kg appears to be a maximum permissible weight,

that the converter must have relatively high efficiency and this condition cannot readily be satisfied in the case of small sizes, especially if intermediate components are to be included between the driving elements and receiving elements,

that total reliability must be ensured despite the fact that it is impossible to lubricate some of the driving parts which are in contact with the thermodynamic fluid,

that the power cycle of the receiving machine (pumping device) which is intended to reconstitute approximately the pressure curve of the human heart is very different both in periodic time and power distribution from the cycle of conventional rotary driving machines. Inertia, speed reduction or solid or fluid transmission must accordingly be introduced and have the effect of increasing the weight, reducing mechanical efficiency and making it more difficult to achieve reliability.

The object of the invention is to provide an implantable artificial heart which meets practical requirements more effectively than those of the prior art, especially insofar as the difficulties referred to above are reduced to a considerable extent.

To this end, the invention proposes an implantable artificial heart essentially comprising a hydraulic device for producing the blood-moving pressure which is driven by a rapid-expansion motor and a linear-displacement piston, a relaxation mechanism which is interposed between the driving piston and the hydraulic device and comprises an elastic member such as a spring enclosed between two components which are rigidly fixed in one case to the driving piston and in the other case to the driving member of the hydraulic device, abutment means for limiting the spacing of said components to a value at which the compression of the spring corresponds to maintenance of the pressure at the end of the systole phase by means of the pump, means for temporarily locking the component which is coupled to the driving piston in the state of maximum extension of said piston during the working stroke thereof and a member which initiates unlocking of said means at the end of expansion of the spring.

The motor must be of a type which absorbs only a small amount of energy during the non-propelling portion of the cycle (systole). It is possible in particular to employ a Rankine or Him-cycle motor which provides in addition to its simplicity of adaptation to this purpose the advantage of readily obtaining a constant pressure (that of the condenser) within the casing of the device and consequently of permitting easy regulation during the diastole phase.

A clearer understanding of the invention will be obtained from the following description of exemplified embodiments of the invention which are given solely by way of example,

7 reference being made to the accompanying drawings, in

which:

FIG. 1 is a general diagram of a group of four cardiac modules which carry out all the functions of the physiological heart;

FIG. 2 is a diagrammatic illustration of the motor and the device for transmitting the power generated by the motor to the cardiac modules;

FIG. 3 is a curve which is representative of the pressures delivered by the ventricular cardiac modules of the embodiment which is illustrated in FIGS. 1 and 2;

FIG. 4 is similar to FIG. 2 and is a vertical central sectional view showing an alternative form of construction.

The implantable artificial heart may be regarded as being constituted by four sub-assemblies which will be discussed successively: the blood-pumping sub-assembly which is constituted by cardiac modules and a pump for actuating said cardiac modules (as shown in FIG. 1), the motor and the relaxation mechanism for transferring energy (as shown in FIG. 2). Pumping sub-assembly The pumping sub-assembly which is illustrated diagrammatically in FIG. 1 is intended to ensure both pulmonary circulation and general circulation. The sub-assembly comprises four cardiac modules corresponding to the left and right auricles 106 and 10D and to the left and right ventricles 126 and 12D. Each module which is shown is of a known type consisting of a shell 14 having an opening which provides a communication with a control fluid and an opening which provides a communication with a connecting duct 16 or 18. A flexible diaphragm 20 provides within each shell 14 a separation between a compartment 22 containing the pressure-transmission liquid and a compartment 14 which contains the blood. Said diaphragm as well as that part of the shell which is in contact with the blood is lined with dacron velvet on which the fibrin is deposited.

As shown in FIG. I, the duct 18 is mounted between the vena cava and the pulmonary artery and connected to the right auricle 10D and to the right ventricle 12D. Artificial ball valves 26 which are placed in the duct 18 have a function which is similar to that of the valves of a natural heart. The duct 16 is mounted in a similar manner between the pulmonary vein and the aorta and connected to the left auricle 106 and to the left ventricle 12G.

The hydraulic control sub-assembly is associated with the modules. This sub-assembly actuates the ventricles and the au ricles in a wholly synchronous manner so that, on the one hand, the two ventricles are in a maximum blood-filling phase whereas the two auricles are in a minimum blood-filling phase and that, on the other hand, the sum of volumes of circulating blood contained in the ventricles and auricles is constant.

This result is achieved by means of the assembly which is illustrated in FIGS. 1 and 2 and comprises a double piston 28 which moves under the action of a rod 30 while displacing the same quantity of intermediate liquid within two concentric chambers 32 and 34. The first chamber is cylindrical and the second chamber is annular and placed around the first. The system is so designed that the supply of energy to the piston 28 takes place at the time of displacement of this latter in the direction of the arrow f. The intermediate liquid contained in the chambers 32 and 34 is then put under pressure and discharges the blood contained in the ventricles 12D and 126. The same intermediate liquid contained in a single chamber 36 which is limited by the other face of the piston 28 also draws blood at the same time from the auricles 10D and 106. When the blood which displaces the piston 28 is reversed, the auricles are emptied into the ventricles. The displacement of the piston in the direction of the arrow f corresponds to the systolic period and the return corresponds to the diastolic period.

It is apparent that, without any external application of force to the rod 30 at the time of filling of the ventricles, the piston is in substantially indifferent equilibrium irrespective of the conditions of pressurization of the body by reason of the fact that the blood which is supplied through the veins is at a pressure which is established by the ambient pressure. As a first approximation, only the elasticity of the flexible diaphragrns of the shells and the resultant of the pressure forces on the passage of the rod 30 exert a restoring force if no force is applied to the extremity of the piston-rod 30. This property is of considerable significance since forces of only very low value need therefore be applied in order to return the piston to the beginning of its working stroke.

The sub-assemblies which are illustrated in FIG. 1 constitute an extremely complete pumping system. In some cases, it may be found necessary for practical reasons to adopt simplified solutions and in particular the following:

the right-hand circulation section (ventrical 12D, auricle D and compartment 34) can be dispensed with: the principle which has already been described remains the same. The double piston is accordingly replaced by a single piston,

the two auricles can be dispensed with and the intennediate liquid within the compartment 26 can be replaced by a fluid in which the liquid and vapor phases are brought together and which is such that the vapor pressure is substantially equal to the blood pressure in the diastole phase. One of the drawbacks of this arrangement clearly lies in the fact that the equilibrium of the piston is no longer indifferent at the time of its return irrespective of the pressurization of the body. Fever can also destroy the indifferent equilibrium of the piston,

the auricles 10D and 100 can be dispensed with as well as the wall which isolates the chamber 36 from the mechanism at the pressure which prevails within the motor casing. In this case, it is found necessary to apply to the piston the action of a spring which has a low stiffness coefficient in order to compensate for the difference between atmospheric pressure and the pressure p within the motor casing, this pressure being equal to the pressure of the condenser and therefore chosen so as to be as low as possible in order to increase the efficiency.

Said spring restores the indifferent equilibrium of the piston at the time of its return. Again in this alternative embodiment, the equilibrium of the fluid is responsive to the blood pressure upstream of the heart and will be modified if the person who is carrying the heart moves to a higher altitude. This spring can be dispensed with by establishing a pressure p which is close in value to that of the blood but in that case the efficiency of the device is appreciably reduced.

Finally, the pump which serves to actuate the cardiac modules can be constituted by two opposite pistons having symmetrical motion of the type designated by the reference 28. This design solution entails the use either of two motors and two synchronized relaxation mechanisms of the type mentioned hereinafter or of a single motor and a single relaxation system to which should be added a transmission device for producing the symmetrical movements.

Motor The motor will be described only very briefly since it is of the conventional Rankine-cycle type. The motor is illustrated diagrammatically in FIG. 2 and comprises a boiler which is heated by an alpha radioisotope source. It is possible in particular to employ a plutonium-238 source containing approximately 30 g of radioactive material. Said source 40 is placed within the boiler 42 proper. The boiler 42 communicates with a cylindrical expansion chamber 44 via an admission valve 46 which is thrust back towards its seat by elastic restoring means represented by a spring. At the end of its working stroke, a piston 48 which is placed within the cylinder 44 uncovers ports 50 through which the expanded vapor is exhausted into the casing 52 which contains the motor and the relaxation mechanism. The top end-wall of said casing constitutes a capillary condenser 54 which is cooled by the intermediate liquid (this liquid being in turn cooled by the blood). The walls of the casing 52 are also provided with a capillary network in order to return any trace of condensation to the condenser 54. The use of this arrangement permits operation in all orientations of the heart. The condensed liquid is returned to the boiler 42 through a suction tube 56 fitted with check valves 57 and a lift and force pump which will be described hereinafter. The boiler 42 and the cylinder 44 are heat-insulated by means of layers 58 of thermal insulation material.

The motor is of known type and therefore does not call for any extended description. It need only be noted in addition that, although some organic liquids can be contemplated, water appears to be the most suitable working fluid at the present time. In the case of water, a pressure at the condenser of the order of O. bar is preferably adopted.

The piston 48 can be fitted with a mechanism for maintaining the admission valve 46 in the open position. Once the valve has been dislodged from its seat by the piston during the return stoke of this latter, it is in fact an advantage to complete the force of attraction produced by the armatures 76 and the magnets 78 (which will be described later) by means of an elastic force which is produced by a complementary mechanism. Said mechanism can be arranged as illustrated in FIGS. 5 and 6. In FIG. 5 the magnetic spring is a magnet 110 carried by the piston and a magnet 112 carried by the guide rod of valve 108, the opposed poles of magnets 110 and 112 having opposite polarity. In FIG. 6 the structure comprises a push-rod 122 which is capable of moving within the piston between a position in which said rod projects from this latter (as shown in full lines in FIG. 6) and a position in which it penetrates into the piston.

Elastic means is constituted in the embodiment illustrated in FIG. 6 by a magnet 124 which is carried by the piston 48 and by a ferromagnetic washer 126 of the push-rod tend to bring this latter to a projecting position. Leak-tightness is ensured by the plug 130 which is held in position by means of the circlip 132.

The operation of the mechanism accordingly takes place as follows: when the piston reaches the end of its return stroke, the push-rod 122 comes into contact with the valve and penetrates into the piston since the stiffness of the magnetic spring which maintains said push-rod in the projecting position is not sufiicient to overcome the pressure forces which are exerted on the valve 46. The boss 134 then comes into contact with the valve 46 and unseats this latter. The pressures are balanced on each side of the valve 46 and the push-rod 122 returns to the projecting position, lifts the valve 46 to a further extent and maintains it in the open position until the piston 48 has again moved away from the valve.

Relaxation mechanism Finally, it should be noted that the arrangements illustrated in FIGS. 5 and 6 can be employed at the same time but it is evidently not possible to place these systems in alignment with each other.

The driving piston 48 is coupled with the double piston 28 by means of the relaxation mechanism. This mechanism comprises a first supporting member 60 which is rigidly fixed to the driving piston, a second supporting member 62 which is rigidly fixed to the rod 30 of the piston 28 and a spring 64 which is compressed between the members 60 and 62. These two members are provided with abutment flanges 66 and 68 which cooperate with each other in order to limit the expansion of the spring 64 to a value at which its residual compression force corresponds to establishment of the blood pressure at the end of the systole phase. When the flanges are abuttingly applied against each other, the members 60 and 62 therefore constitute two components of a cage which encloses the spring. The member 60 carries a resilient catch 70 which is intended to engage a bearing stop 72 provided on the casing 52 when the piston 48 completes its working stroke which is accompanied by the compression of the spring 64. So far as the member 62 is concerned, said member carries an arm 74 which releases the catch 70 when the expansion of the spring 64 is completed. Instead of the locking system comprising a resilient catch and bearing stop as illustrated in FIG. 2, it would be possible to employ a system comprising magnets and backplates which casing 52.

In the embodiment which is illustrated in FIG. 2, the member 60 further carries magnetic back-plates 76 which are attracted on completionof the return stroke of the piston 48 by magnets 78 which are secured to the casing 52.

The lift and force pump for re-injecting condensate into the boiler makes use of the relative displacements of the members 60 and 62. Said pump comprises a plunger 80 and a cylinder 82. The plunger 80 is connected to an enlarged end portion of the rod 30 by means of one or a number of rods 84 (only one of these latter being shown in FIG. 2). The cylinder 82 which is secured to the cylinder 44 by means of a jacket 86 having open portions also constitutes a guide bearing for the rods 84. Moreover, leak-tightness between two media having different functions within the pumping sub-assembly must in all cases be absolute. Although flexible rolling seals are contemplated for this purpose, other means may be adopted by way of alternative. ln FIGS. 2 and 4, these seals are designated by the reference numerals 31, 33, 35, 37 and 31', 33', 35', 37 and 39.

The operation of the artificial heart which is illustrated in FIGS. 1 and 2 will now be described with reference also to FIG. 3. Since cardiac modules are known per se, only the operation of the assembly consisting of motor and relaxation mechanism will be discussed in detail.

A complete working cycle will be described on the assumption that the components are initially located in the following positions: the driving piston 48 is in the bottom position, the valve 46 is lifted, the abutment flanges 66 and 68 are in contact with each other and maintain the spring 64 in precompression, the magnetic back-plates 76 are applied against the magnet 78. The pressures within the chambers 32, 34 and 36 are substantially equal to the blood pressure during the natural diastole phase (4 to 5 mm of mercury).

Expansion accordingly takes place as follows. The vapor under pressure which penetrates into the cylinder 44 abruptly accelerates the piston 48 which is braked only by the force of the spring 64. The valve 46 closes and the vapor expands during a rapid phase during which the piston 48 and associated components accelerate then decelerate and finally come to a standstill at the end of travel by engagement of the catch 70 on the bearing stop 72.

During this phase which is very short by reason of the low inertia of the driving piston 48 and associated components relative to the forces applied by the vapor and the spring 64, the double piston 28 is practically motionless. However, as a result of the compression of the calibrated spring 64, the intermediate liquid which is present within the chambers 32 and 34 has been put under pressure.

are carried by the members 60, 62 and the This initial phase as shown from the time t to the time t in FIG. 3 corresponds from the thermodynamic point of view to the propulsion phase of the driving cylinder and from the medical point of view to the isometric phase in which the blood is put under pressure within the two ventricles 12D and 12G. The ratio between the pressures within the chambers 32 and 34 is establishedautomatically at the correct value since it is fixed 'by the resistances of the two natural circulation systems of the human body. Only the resultant of the pressure forces on the double piston 28 is imposed since it is practically equal to the force supplied by the spring 64 in its state of maximum compression in which said spring is shown in FIG. 2 (end of the thermodynamic propulsion period and beginning of the systole) by reason of the very short duration of the time interval 1, t 0 which is exaggerated in FIG. 3 for the sake of enhanced clarity.

The following stage of operation corresponds to the expansion of the spring 64. The driving piston 48 and associated components are rendered motionless by the catch 70 which is held in position under the pressure of the spring 64. From the thermodynamic standpoint, the initial part of said phase corresponds to the exhaust of vapor through the ports 50 which, in a standard cycle, remain uncovered for approximately onethird of a second. From the mechanical standpoint, the spring 64 is applied against the member 60, drives the double piston 28 downwards and discharges the intermediate liquid contained in the chambers 32 and 34. From the medical standpoint, this phase of operation corresponds to the systole. In practice, the duration of this phase is set on the one hand by the resistance offered by the circulatory system of the human body and on the other hand by the force-compression characteristic of the spring 64. By virtue of a suitable choice of said spring, the device is capable of providing a systole period t, t, (as shown in FIG. 3) which is practically equal to that of the human heart and a decrease in pressure during the systole period which is similar to the shape of the corresponding curve in the case of the human heart.

At the end of this phase, the pressures which prevail within the ventricles 12G and 12D (corresponding to the points A and B on the curve of FIG. 3) are in a ratio which is imposed by the resistances of the circulatory systems as is the case throughout the duration of the phase.

At the final moment of the phase of expansion of the spring, the abutment flanges come into contact and prevent any subsequent action of the spring. After closure of the valves 26, the pressures within the chambers 32 and 34 therefore drop abruptly to a value which is practically equal to that of the blood in the diastole period (point C in FIG. 3). At the same time, the pressure force exerted by the catch 70 on its stop 72 becomes very low and the arm 74 which has moved during extension of the spring releases the catch. Thereupon, all the components which are connected to the driving piston 48 and to the double piston 28 once again form a rigid assembly which is capable of moving as a single unit along the axis of the cylinder 44.

The moving system as thus constituted then returns as a single unit towards its initial position under the action of the resultant of the pressure forces, especially by virtue of the passage (to be chosen accordingly) of the rod 30 and if necessary of the elasticity which is given to the shell diaphragms. The addition of a light spring may prove necessary. By reason of the fact that, in practice, fluid friction alone prevents the return of the double piston, these forces of small amplitude are sufficient to bring the moving system back to its initial position. In the embodiment which is illustrated in FIG. 2, a complementary restoring action can be provided by the magnets 78 and the magnetic back-plates 76 when these elements move towards each other although the essential function of these latter is thermodynamic.

In fact, from the thermodynamic viewpoint, the phase last mentioned corresponds to recompression of the working fluid which remains within the cylinder 44. As a result of its inertia and the action of the magnets 78, the moving system causes forcible opening of the admission valve 46 at the end of the return travel of said system. Accordingly, the bottom face of the piston 48 is provided with an abutment extension 88. The initial conditions are thus restored.

From the medical viewpoint, the phase just mentioned corresponds to the diastole period (filling of the ventricles owing to the displacements of the intermediate fluid and to the action of the artificial valves 26). During this last phase, the blood pressure is imposed by the body itself.

Condensation of the vapor which is discharged through the port 50 takes place continuously within the capillary condenser 54. The small drops which may appear on the walls of the casing 52 are returned to the condenser by capillarity.

There is evidently associated with the artificial heart which has just been described a regulating system which controls the length of the diastole period in dependence on physiological data of the patient who carries the artificial heart. This regu' lating operation can be carried out by modifying the diastole period t (FIG. 3). To this end, provision can be made for a system which retards the return of the moving system by dissipation of energy, for example on the path followed by the intermediate fluid which passes from the chamber 36 to the auricles, or by braking of the rod 30. The boiler is designed for the maximum power to be supplied (of the order of 2 to 3 W by reason of the fact that reduced activity may be imposed on the carrier of an artificial heart and therefore has constant power). It is clearly necessary to eliminate vapor from the boiler at low load and this can be achieved automatically by regulating the pressure by means of a vapor discharge through a calibrated valve (not shown) in the casing 52 of the device.

FIG. 3 shows that the pressure curve provided by the implantable artificial heart which has just been described reconstitutes the curve of the real cardiac beat to a sutficient degree of approximation to be acceptable. This result is attained by virtue of very simple means which are essentially constituted by a spring-type relaxation mechanism and without introduction of parts having very high inertia. By way of example, the relaxation mechanism can be associated with a motor having an expansion within the range of 50 bars to l bar approximately, thereby resulting in a force at the beginning of projection of the piston 48 which is'of the order of 150 kgs. The relaxation mechanism reduces this initial force to a value which is wholly compatible with the strength of the arteries.

A further advantage of the device should also be noted and this is related to the fact that the moving system comprising the double pistons 28 and the driving piston 48 is in substantially indifferent equilibrium at the time of its return travel and that the resultant of the forces can readily be adjusted. This property permits of easy regulation and results in a stable device.

The alternative embodiment of the invention which is illustrated in FIG. 4 differs essentially from that of FIG. 2 in the arrangement of the lift and force pump for re-injecting the condensate into the boiler. For the sake of greater simplicity, the corresponding components of the embodiments of FIGS. 2 and 4 are designated by the same reference numerals followed by the prime index in FIG. 4.

There is shown again in FIG. 4 a member 82' which, in this case, does not constitute the cylinder of the lift and force pump but only a guide bearing for an extension 90 of the rod 30; this makes it possible to dispense with the guide bearing 92 of the rod 30 which was provided in the embodiment of FIG. 2.

The rod is provided above the double piston 28 with an extension 94 which is rendered leak-tight by means of a seal 39, said extension being guided by a bearing 96 which is rigidly fixed to the casing and by a piston 98 which moves within a reinjection pump cylinder 100, said cylinder being also rigidly fixed to the casing. The condensate is supplied to the pump through a pipe 102 fitted with a check valve and then discharged to the boiler through a second pipe 104 which is also fitted with a check valve. A small pipe 106 permits pressure balancing between the two parts of the mechanism.

It should also be pointed out that a number of assemblies of the type shown in FIGS. 2 and 4 can be associated in order to prevent shocks which give rise to inertia forces having a component parallel to the axis and which could not be tolerated by the patient. With this objective, it is only necessary to adopt a symmetrical arrangement which can comprise two motors for driving by means of relaxation mechanisms two hydrauliccontrol sub-assemblies which are grouped together in a single central block. The movements are made strictly symmetrical by means of a link-rod system. The arrangement can be reversed and provision accordingly made for two motors in a central block, with the result that only one admission valve is required for both motors.

I claim:

1. An implantable artificial heart comprising: a hydraulic transmission device for imparting a moving pressure to the blood; a prime mover having a linear displacement driving piston having a rapid working stroke; and a relaxation mechanism mechanically coupling the driving piston and the hydraulic device, said mechanism having resilient means which is compressed between a first and a second components respectively secured to said driving piston and to a driving member of the hydraulic device and whose compression corresponds to the blood pressure at the beginning of systole when said two components are in their position closest to each other, abutment means for limiting the spreading of said components to a distance at which the compression of said resilient means corresponds to the pressure at the end of the systole phase, means for temporarily locking said first component upon arrival of said piston at the end of the working stroke thereof, and a member for releasing said locking means upon substantially complete expansion of the resilient means.

2. A heart in accordance with claim 1, wherein the prime mover is a Rankine-cycle or Him-cycle engine.

3. A heart in accordance with claim 1, wherein the hydraulic device comprises a single piston which is linearly movable within a cylinder and separates two compartments in said cylinder, diaphragm means for separating one of said compartments in two chambers, means for communicating the pressure in said two chambers to left and right ventricular blood, respectively, and means for communicating the liquid pressure in the other of said compartments to auricular blood.

4. A heart in accordance with claim 3, wherein said cylinder is provided with compartments having a geometry such that the return of the piston during the diastole phase is carried out without applying forces of appreciable value.

5. A heart in accordance with claim 1, wherein the temporary-locking means comprise a catch carried by an elastic blade rigidly fixed to the component which is coupled to the driving piston and a stop which is rigidly fixed to the heart casing.

6. A heart in accordance with claim 5, wherein the unlocking means are constituted by a stud rigidly fixed to the component which is coupled to the pump and releases the catch from the stop at the end of the expansion travel of the spring.

7. A device in accordance with claim 1, wherein a radioisotope source supplies heat to the boiler of the motor.

8. An artificial heart in accordance with claim 1, wherein cooperating magnetic means are carried by the casing and by the component which is coupled to the driving piston, said magnetic means being such as to produce action especially at the end of the return stroke of the driving piston in order to return said piston to the starting position while re-compressing the driving fluid which has remained within the cylinder and while ensuring the partial lift of the vapor-admission valve.

9. An artificial heart in accordance with claim 1 wherein the driving piston is fitted with an exhaust valve provided with elastic means for restoring to the open position, said valve being mounted so that the pressure within the cylinder should tend to apply said valve against its seat.

10. An artificial heart in accordance with claim 9, wherein said elastic means for restoring the exhaust valve are constituted by a magnetic spring.

11. An artificial heart in accordance with claim 10, wherein the magnetic spring comprises a magnet carried by the piston and a magnet carried by a guide rod of the valve and the opposite poles of the two magnets have the same polarity.

12. An artificial heart in accordance with claim 1, wherein abutment means carried by the piston cooperate with the moving element of said admission valve in order to lift said valve at the end of the return stroke of the piston.

13. An artificial heart in accordance with claim 1, wherein elastic means carried by the piston are intended to maintain the admission valve in the open position once the moving element of said valve has been displaced from its seat by the piston.

14. An artificial heart in accordance with claim 13, wherein said elastic means comprise a push-rod which is capable of moving axially within the piston and is returned by a magnetic spring to a position in which said push-rod projects from the piston towards the admission valve.

15. An artificial heart in accordance with claim 1, wherein said heart comprises two identical assemblies each constituted by a hydraulic device, a motor and a relaxation mechanism,

said two assemblies being disposed symmetrically along a are grouped together in a central block and have a common common axis. admission valve.

16.v An artificial heart in accordance with claim 15, wherein An tifi i l heart in accordance with claim 5 wherein the two motors are placed on each side of hydraulic devices which are g p mgether within a single block. a lmk rod system provided for synchronizing the operation 17. An artificial heart in accordance with claim 16, wherein of both assembhes' the hydraulic devices are placed on each side of motors which 

1. An implantable artificial heart comprising: a hydraulic transmission device for imparting a moving pressure to the blood; a prime mover having a linear displacement driving piston having a rapid working stroke; and a relaxation mechanism mechanically coupling the driving piston and the hydraulic device, said mechanism having resilient means which is compressed between a first and a second components respectively secured to said driving piston and to a driving member of the hydraulic device and whose compression corresponds to the blood pressure at the beginning of systole when said two components are in their position closest to each other, abutment means for limiting the spreading of said components to a distance at which the compression of said resilient means corresponds to the pressure at the end of the systole phase, means for temporarily locking said first component upon arrival of said piston at the end of the working stroke thereof, and a member for releasing said locking means upon substantially complete expansion of the resilient means.
 2. A heart in accordance with claim 1, wherein the prime mover is a Rankine-cycle or Hirn-cycle engine.
 3. A heart in accordance with claim 1, wherein the hydraulic device comprises a single piston which is linearly movable within a cyLinder and separates two compartments in said cylinder, diaphragm means for separating one of said compartments in two chambers, means for communicating the pressure in said two chambers to left and right ventricular blood, respectively, and means for communicating the liquid pressure in the other of said compartments to auricular blood.
 4. A heart in accordance with claim 3, wherein said cylinder is provided with compartments having a geometry such that the return of the piston during the diastole phase is carried out without applying forces of appreciable value.
 5. A heart in accordance with claim 1, wherein the temporary-locking means comprise a catch carried by an elastic blade rigidly fixed to the component which is coupled to the driving piston and a stop which is rigidly fixed to the heart casing.
 6. A heart in accordance with claim 5, wherein the unlocking means are constituted by a stud rigidly fixed to the component which is coupled to the pump and releases the catch from the stop at the end of the expansion travel of the spring.
 7. A device in accordance with claim 1, wherein a radioisotope source supplies heat to the boiler of the motor.
 8. An artificial heart in accordance with claim 1, wherein cooperating magnetic means are carried by the casing and by the component which is coupled to the driving piston, said magnetic means being such as to produce action especially at the end of the return stroke of the driving piston in order to return said piston to the starting position while re-compressing the driving fluid which has remained within the cylinder and while ensuring the partial lift of the vapor-admission valve.
 9. An artificial heart in accordance with claim 1 wherein the driving piston is fitted with an exhaust valve provided with elastic means for restoring to the open position, said valve being mounted so that the pressure within the cylinder should tend to apply said valve against its seat.
 10. An artificial heart in accordance with claim 9, wherein said elastic means for restoring the exhaust valve are constituted by a magnetic spring.
 11. An artificial heart in accordance with claim 10, wherein the magnetic spring comprises a magnet carried by the piston and a magnet carried by a guide rod of the valve and the opposite poles of the two magnets have the same polarity.
 12. An artificial heart in accordance with claim 1, wherein abutment means carried by the piston cooperate with the moving element of said admission valve in order to lift said valve at the end of the return stroke of the piston.
 13. An artificial heart in accordance with claim 1, wherein elastic means carried by the piston are intended to maintain the admission valve in the open position once the moving element of said valve has been displaced from its seat by the piston.
 14. An artificial heart in accordance with claim 13, wherein said elastic means comprise a push-rod which is capable of moving axially within the piston and is returned by a magnetic spring to a position in which said push-rod projects from the piston towards the admission valve.
 15. An artificial heart in accordance with claim 1, wherein said heart comprises two identical assemblies each constituted by a hydraulic device, a motor and a relaxation mechanism, said two assemblies being disposed symmetrically along a common axis.
 16. An artificial heart in accordance with claim 15, wherein the two motors are placed on each side of hydraulic devices which are grouped together within a single block.
 17. An artificial heart in accordance with claim 16, wherein the hydraulic devices are placed on each side of motors which are grouped together in a central block and have a common admission valve.
 18. An artificial heart in accordance with claim 15, wherein a link-rod system is provided for synchronizing the operation of both assemblies. 